1. Field of the Invention:
The present invention relates to plastic film products, such as sealed bags, wound films, adhesive tapes, etc., having a plurality of scratches or cuts formed along the edges thereof so as to be shallow and small enough to be invisible to the naked eye.
2. Description of the Prior Art:
Plastic films are generally thin, light in weight, soft, excellent in transparency and airtightness, and exhibit high strength and, for these reasons, these are widely accepted for actual use. Further, since plastic sheets have thermal plasticity, it is easy to manufacture laminated plastic having paper, metallic foil, cloth, adhesives or other chemicals attached thereto and, therefore, plastic films find extensive utility in many applications.
Since a laminate having metallic foil and polyvinylidene chloride film attached to other plastic, in particular, is excellent in airtightness and is sufficiently sealed merely by thermal fusion without using any adhesive, it is used as a dispensing bag for accommodation of various kinds of wares such as foodstuffs, medical supplies, small articles, etc. of various forms such as of liquid, powder, paste, solid and so on. However, these sealed dispensing bags have a disadvantage that since the plastic material of which the bags are made has toughness it is difficult to break the seal in taking the contents out of the bags. In spite of such toughness, once the plastic material is injured, the injury tends to be easily propagated. Accordingly, by giving a cut to the edge portion of the bag to be torn open, it is possible for a person to easily break the seal through the cut by applying a stretching force with his fingers.
In consideration of the properties of the plastic material as described above, there have heretofore been adopted a method for forming a cut in advance in the edge portion of the bag attached by fusion and a method for cutting a V-shaped notch in the edge portion. However, the former method is disadvantageous in that the place where the cut portion is formed in the edge portion of the bag cannot easily be found. In the latter method, it is easy to find the V-shaped notch, but the triangular cut pieces are dispersed in effecting the bagmaking and bag-filling treatments on a large scale to thereby make the working environment worse.
In either method, since the number of cuts or the like is limited to one, sometimes the cut is not formed in a desired position and since the cut is propagated in a reluctant direction, the filler may be dispersed to the surroundings. Furthermore, the typical cut of the prior art has a depth of about 2 mm and the cut portion exhibits low impact resistance. For this reason, provision of a great number of such cuts will reduce the strength of bags when distributed or stored and make the manufacturing processes complicated and, therefore, cannot be adopted.
There also exists a plastic sheet product having its entire edge portion formed in the shape of sawteeth. However, since the concave portions of the sawteeth either have relatively obtuse angles or are rounded, the effect of initial cutting cannot fully be expected and, therefore, such a product is not suitable for use as a dispensing bag of a thick film having liquid, emulsion, paste or hygroscopic substances sealed therein.
In the case of wound tapes such as adhesive tapes which are used after cutting a given length of the tape unwound, the toughness, one of the merits of plastic sheets, becomes a demerit because a cutting tool is required. Since such a cutting tool as scissors, a knife, etc. is not always laid in the vicinity of the place where the tape is used, the wound adhesive tape is provided generally with a cutter having sawteeth. The sawteeth often graze the user's fingers to be injured. What is worse, since the cut end of the tape is corrugated, the tape is apt to be torn in the lengthwise direction in the subsequent unwinding of the tape, thus bringing about a great cause of the user's failure in unwinding the tape.
As for adhesive tapes capable of being manually cut with the user's fingers without using any cutting tool, there have heretofore been suggested those made of a thin film, a laterally drawn material, etc. It goes without saying that the thin film allows the strength and reinforcement of the tape to be reduced. Although a thin film tape having the rear surface thereof reinforced with paper has been suggested, it is behind a thick plastic film tape in terms of strength.
Plastic tapes having their entire surfaces satinized by sandblasting, on which any letter or symbol can be written with writing tools such as pencils etc., are available on the market. Letters and symbols remain on the tape due to the filling of the components of a writing tool into the concaves of the satinized surface. However, since the tapes of this kind are much inferior in strength and do not have sufficient reinforcing effects, these are used merely in the form of adhesive labels bearing optional letters and/or symbols thereon.